Endothelial cells synthesize IGF BP2-4 and have mRNA for IGFBP2-6. IGFBP-3 and IGFBP-5 associated with the endothelial cell surface and extracellular matrix. A basic segment of IGFBP-3 and IGFBP-5 is critical for this monolayer binding of IGFBP-3 and IGFBP-5. We are synthesizing several peptides to the determine the structural specificity of the C-terminal basic region of the IGFBPs and require mass spectrometry to confirm molecular weight.